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diff --git a/HOWTO b/HOWTO
index 1176d228..c9d29f29 100644
--- a/HOWTO
+++ b/HOWTO
@@ -264,6 +264,10 @@ ioengine=str	Defines how the job issues io to the file. The following
 				we use read(2) and write(2) for asynchronous
 				io.
 
+			null	Doesn't transfer any data, just pretends
+				to. This is mainly used to exercise fio
+				itself and for debugging/testing purposes.
+
 iodepth=int	This defines how many io units to keep in flight against
 		the file. The default is 1 for each file defined in this
 		job, can be overridden with a larger value for higher
@@ -315,7 +319,13 @@ prioclass=int	Set the io priority class. See man ionice(1).
 
 thinktime=int	Stall the job x microseconds after an io has completed before
 		issuing the next. May be used to simulate processing being
-		done by an application.
+		done by an application. See thinktime_blocks.
+
+thinktime_blocks
+		Only valid if thinktime is set - control how many blocks
+		to issue, before waiting 'thinktime' usecs. If not set,
+		defaults to 1 which will make fio wait 'thinktime' usecs
+		after every block.
 
 rate=int	Cap the bandwidth used by this job to this number of KiB/sec.
 
@@ -353,11 +363,41 @@ mem=str		Fio can use various types of memory as the io unit buffer.
 			shm	Use shared memory as the buffers. Allocated
 				through shmget(2).
 
-			mmap	Use anonymous memory maps as the buffers.
-				Allocated through mmap(2).
+			shmhuge	Same as shm, but use huge pages as backing.
+
+			mmap	Use mmap to allocate buffers. May either be
+				anonymous memory, or can be file backed if
+				a filename is given after the option. The
+				format is mem=mmap:/path/to/file.
+
+			mmaphuge Use a memory mapped huge file as the buffer
+				backing. Append filename after mmaphuge, ala
+				mem=mmaphuge:/hugetlbfs/file
 
 		The area allocated is a function of the maximum allowed
-		bs size for the job, multiplied by the io depth given.
+		bs size for the job, multiplied by the io depth given. Note
+		that for shmhuge and mmaphuge to work, the system must have
+		free huge pages allocated. This can normally be checked
+		and set by reading/writing /proc/sys/vm/nr_hugepages on a
+		Linux system. Fio assumes a huge page is 4MiB in size. So
+		to calculate the number of huge pages you need for a given
+		job file, add up the io depth of all jobs (normally one unless
+		iodepth= is used) and multiply by the maximum bs set. Then
+		divide that number by the huge page size. You can see the
+		size of the huge pages in /proc/meminfo. If no huge pages
+		are allocated by having a non-zero number in nr_hugepages,
+		using mmaphuge or shmhuge will fail. Also see hugepage-size.
+
+		mmaphuge also needs to have hugetlbfs mounted and the file
+		location should point there. So if it's mounted in /huge,
+		you would use mem=mmaphuge:/huge/somefile.
+
+hugepage-size=siint
+		Defines the size of a huge page. Must at least be equal
+		to the system setting, see /proc/meminfo. Defaults to 4MiB.
+		Should probably always be a multiple of megabytes, so using
+		hugepage-size=Xm is the preferred way to set this to avoid
+		setting a non-pow-2 bad value.
 
 exitall		When one job finishes, terminate the rest. The default is
 		to wait for each job to finish, sometimes that is not the